The present invention relates to a method for making polyalkylated xanthenes.
Chazan et al., Bull. Soc. Chim. Fr., 1968, 1384, report that condensation of acetone and phenolic material in the presence of phosphorous oxychloride provides a 2.5% yield of tetramethylxanthene. Early observations by Niederl, Angew. Chem., 44, 467 (1931), and Baker et al., J. Chem. Soc.,1939, 195, and J. Chem. Soc., 1951, 76, show that when acetone is exposed to m-cresol in the presence of cold concentrated sulfuric acid, a spirobichroman of the formula ##STR1## is formed. However, when HCl is used as a catalyst in a mixture of m-cresol and acetone, a chroman of the following formula is formed: ##STR2##
It would be desirable to provide a method for effecting reaction between alkylated phenol and acetone to produce polyalkykated xanthenes at high yields.
It also would be desirable to be able to convert condensation products, such as spirobichromans or chromans, which are formed by reacting acetone and alkylated phenols to polyalkykated xanthenes.
As used hereinafter, the term "alkylated phenol" means a phenol having one or two C.sub.1-4 alkyl radicals. Among the preferred alkylated phenols, there are included m-cresol, p-cresol and 3,4-dimethylphenol.